atq and at -l (40.9)
are more important than they seem. They give
you a way to decide when to run your jobs. I suggest that you
check atq before picking a time to run your job. If you don't,
the system may have a dozen huge jobs starting at midnight or 1 a.m.
They will bring the system to its knees when there's no one around to
help out. Here's an example of what can happen, using the BSD-style
at commands:

Four of the five users happened to pick 1 a.m. as their submission time.
Therefore, four big jobs will start in the middle of the night. Will
your system survive? Will any of these be done in the morning? These
are good questions. Instead of submitting your jobs to run
at 1 a.m., at midnight, or at some other integral number, start them
at different times, and make them times like 3:48 a.m. If your system
administrator notices lots of jobs running at the same times on your
system, she might delete some of them and ask you to reschedule.

If your system has
personal crontab files (40.12),
you won't be able to see other users' cron jobs.
The best way to cut system load is to pick strange times like 4:37 a.m.
for your cron jobs.